Added a page to document how to use image data. (#969)

Author: dasjo

doc/queries/images.md

@@ -0,0 +1,66 @@
+The following examples should help accessing images and their derivatives based on image styles:
+
+## Add the schema declaration
+
+```gql
+type Article implements NodeInterface {
+...
+  image_url: String
+  image_alt: String
+  image_thumbnail: Image
+  image_large: Image
+...
+}
+
+type Image {
+  url: String
+  width: Int
+  height: Int
+}
+```
+
+## Adding resolvers
+
+```php
+    $registry->addFieldResolver('Article', 'image_url',
+      $builder->compose(
+        $builder->produce('property_path')
+          ->map('type', $builder->fromValue('entity:file'))
+          ->map('value', $builder->fromParent())
+          ->map('path', $builder->fromValue('field_image.entity')),
+        $builder->produce('image_url')
+          ->map('entity', $builder->fromParent())
+      )
+    );
+
+    $registry->addFieldResolver('Article', 'image_alt',
+      $builder->produce('property_path')
+        ->map('type', $builder->fromValue('entity:node'))
+        ->map('value', $builder->fromParent())
+        ->map('path', $builder->fromValue('field_image.alt'))
+    );
+
+    $registry->addFieldResolver('Article', 'image_thumbnail',
+      $builder->compose(
+        $builder->produce('property_path')
+          ->map('type', $builder->fromValue('entity:file'))
+          ->map('value', $builder->fromParent())
+          ->map('path', $builder->fromValue('field_image.entity')),
+        $builder->produce('image_derivative')
+          ->map('entity', $builder->fromParent())
+          ->map('style', $builder->fromValue('thumbnail'))
+      )
+    );
+
+    $registry->addFieldResolver('ProductDetailPage', 'image_large',
+      $builder->compose(
+        $builder->produce('property_path')
+          ->map('type', $builder->fromValue('entity:file'))
+          ->map('value', $builder->fromParent())
+          ->map('path', $builder->fromValue('field_image.entity')),
+        $builder->produce('image_derivative')
+          ->map('entity', $builder->fromParent())
+          ->map('style', $builder->fromValue('large'))
+      )
+    );
+```